This invention relates generally to EMI shielded electrical cables and connectors and more particularly to double-ended or feedthrough electrical connectors and EMI shielding thereof. Specifically, the present invention relates to a connector assembly for terminating a double-shielded electrical cable and for maintaining the integrity of the EMI double-shielding system throughout the entire connector assembly to provide total and continuous EMI shielding thereof.
Electromagnetic interference (EMI) shielded cables and connector assemblies are frequently used for the transmission of data signals between programmable instruments, such as computers and the like, as well as in other environments wherein electrical and electromagnetic radiation can be expected to interfere with the electrical signals carried by the interconnecting cables and connector assemblies. An example of such a data transfer system is disclosed in U.S. Pat. No. Re. 29,246. EMI shielding is utilized in such cables and connector assemblies to receive EMI radiation emitted by nearby instruments and cables, thereby preventing such radiation from completely penetrating the cables and connector assemblies and being received by the internal conductors and contact elements thereof. In environments containing a large number of such programmable instruments, the intensity of EMI and electrical radiation is generally high, and proper shielding of the interconnecting cables and connector assemblies is critical.
A wide variety of shielded cable and connector assembly arrangements have been developed over the years for various purposes. Such cables generally include a layer of electrically conductive material disposed about the conductors of the cable with the stray EMI radiation being received by and conducted along the separate electrical circuit of the shielding layer. Likewise, when such cables are terminated to a connector assembly, the cable's EMI shield is generally grounded to an electrically conductive connector assembly housing so as to shield the terminal portions of the conductors as well as the contact elements disposed in the connector assembly. However, in high intensity EMI radiation fields, such single layer shielding protection has generally proven inadequate. It has been shown that in such environments, some of the stray EMI and electrical radiation occasionally penetrates the single shielding layer and is received by the cable conductors and assembly contact elements, which reception interferes with the electrical signals being transmitted therealong. Furthermore, such single layered shielding protection does not adequately prevent electrical and EMI radiation emissions by the shielded cable and connector assemblies themselves, which emissions can interfere with the signals carried by other proximately disposed cables and connector assemblies.
The interconnection of programmable instruments also occasionally requires the termination of a shielded cable to a double-ended or feedthrough type connector assembly, as seen in the IEEE Standard Digital Interface for Programmable Instrumentation manual, IEEE Standard 488-1975. In this regard, it is known to provide a pair of connector members at the end of each cable which are arranged in a back-to-back relation. Examples of such double-ended connectors are illustrated in U.S. Pat. Nos. 3,705,388, 3,866,292, 3,876,276 and 3,963,300, and U.S. Pat. Application Ser. No. 798,781. However, prior to the present invention, such double-ended connector assemblies have not included EMI shielding. Therefore, even though an EMI shielded cable may adequately protect the conductors therein from stray EMI and electrical radiation, the termination of such a cable to an unshielded double-ended connector assembly substantially reduces the overall shielding capability of the cable and connector assembly unit. Thus, any shielding protection provided by the cable is substantially diminished by the termination of such a cable to an unshielded double-ended connector assembly.